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Glossary

Bennett’s injury is a fracture subluxation. The causative mechanism is axial
overload along the first metacarpal with simultaneous flexion. The palmar
oblique ligament holds the palmar marginal fragment in its anatomical
position.

The distal part of the first metacarpal is adducted and supinated by
adductor pollicis. The metacarpal as a whole is also displaced proximally by
the abductor pollicis longus muscle.
The treatment goals are to reposition the first metacarpal in the
carpo-metacarpal joint, and to restore the articular surface.

Teaching video

Inspection of the joint

To determine the exact geometry of the fracture and correct placement of the
screws, it may be helpful to open the fracture plane by exerting traction and
supination on the thumb.
The fracture surfaces must be irrigated for better visualization.

Reduce the fracture by pronation of the metacarpal and hold the reduction
with a pointed reduction forceps.
Under direct vision, check that the joint surface is anatomically reduced, and
adjust as necessary.

K-wire

Drilling for the lag screw

Drill a thread hole through both fragments, using 1.5 mm drill. If a
non-selftapping screw is used, tapping is necessary at this stage.
Then use the larger 2.0 mm drill bit to overdrill the near fragment, creating
the glide hole.
It is sufficient to overdrill only the first few millimeters of the near
fragment. If the glide hole extends into the palmar marginal fragment,
compression will not be achieved.
With smaller marginal fragments, it may be necessary to use a 1.5 mm screw (1.1
mm thread hole; 1.5 mm glide hole).

Insertion of the lag screw

Confirm position and stability using image intensification.
Also assess the stability of the fixation under direct vision.
The K-wire is now cut off below the skin, just above the cortex. Bending of the
K-wire risks producing fragment displacement.

Inside-out glide holes

In case of a large palmar marginal fragment, two screws are used.
Before reduction, supinate the metacarpal and drill two glide holes outwards
from the fracture surface for more accurate positioning of the lag screws,
perpendicular to the fracture plane, and evenly placed in the marginal
fragment.

Reduce the fracture

After drilling the glide holes, reduce the fracture by pronation of the
metacarpal, and secure with pointed reduction forceps.
Check the articular reduction under direct vision and using image
intensification.

Drill thread holes

Insert screws

Insert two 2.0 mm self-tapping lag screws and alternately tighten them.
Remove the reduction forceps.
Confirm position and stability using image intensification. Also assess the
stability of the fixation under direct vision.